12 lead motors are becoming more available and some motor manufacturers are selling 12 lead exclusively.
The reason being that twelve lead motors can be used in almost any situation. Soft start's, Drives, wye/delta starting,ect....
Wye/Delta starting is the most common. The only time you have to connect a twelve lead motor in both configs is when a wye/delta contactor config is present.
With across the line starting and drives you always use the RUN Delta connection.
A twelve lead motor cannot operate in the wye config for any application except for starting.
If you apply power to the motor in the wye config, you will produce half the Hp only. The current will look great too. But within a few hours or minutes the motor will let the smoke out.
Always use the delta unless you have the wye/delta config (3)contactor arrangement.
Six lead IEC (metric) motors are sometimes dual voltage rated. Here, the high voltage would be the wye, and the low voltage would be the delta.
